Age-Related Differences in Subset Composition and Activation Responses of Intestinal Intraepithelial and Mesenteric Lymph Node Lymphocytes from Neonatal Swine

Interesting differences were found in the phenotypes and functional responses of intestinal intraepithelial lymphocytes (IEL) and mesenteric lymph node lymphocytes (MLN) from neonatal swine aged 15 to 47 days. IEL and MLN differed significantly in their proliferative responses to the mitogens concanavalin A (Con A) and phorbol ester with ionophore (TPA/ionomycin) and to the cytokine, interleukin 2 (IL-2). IEL did not proliferate well in response to Con A, yet they were able to initiate a high proliferative response to exogenous IL-2, suggesting previous activation. In addition, the IEL response to TPA/ionomycin was very low unless the concentration of ionomycin was increased. With increasing age of the animals, response of the IEL increased. This IEL developmental response pattern was associated with a significant age-related change in T cell phenotype from CD2-4-8 cells to CD2+4-8- cells. In contrast to IEL, proliferation of MLN to Con A and TPA at a lower ionomycin concentration was significant and not influenced by age. Unlike the IEL, MLN were unresponsive to exogenous IL-2. Similar to IEL, they produced very little IL-2 in response to Con A stimulation. Both lymphoid tissues contained 70% T cells and in the MLN more cells were CD4+ or CD4+8+ and fewer were CD4-8- compared to the IEL. These differences between IEL and MLN in neonatal swine may reflect differences not only in the state of cell activation related to the in vivo microenvironment, but also the nature of responsive cell types in each lymphoid tissue.